1. Field of the Invention
The present invention generally relates to characterization of material properties and, more particularly, to characterization of a material's electrical properties.
2. Background of the Invention
In order to conserve battery life, today's mobile communication devices transmit RF signals at relatively low power levels. Moreover, these devices typically transmit at frequencies in the upper MHz range (e.g. 900 MHz) or lower GHz range (e.g. 1.8 GHz). RF signals transmitted at these frequencies are especially susceptible to the influences of nearby structures, for instance walls and roofs of buildings. In particular, materials from which the structures are made often attenuate and scatter the RF signals, thus degrading signal propagation characteristics. Such signal degradation should be considered when determining transceiver locations for a wireless communication system.
The effect of a single homogenous material on an RF signal is typically determined by the electrical characteristics of the material, for instance the materials dielectric constant and loss tangent. However, structures are rarely constructed from a single homogenous material, and the electrical characteristics of different structural materials can vary greatly. For example, the electrical characteristics of concrete are different than the electrical characteristics of aluminum, wood or fiberglass insulation. Further, the electrical characteristics of a material can vary according to density variations within the material. Thus, it is difficult to estimate the true effect of a building on RF signal propagation, and typical assumptions can lead to poor system design.
Coaxial probes and other probes having short antennas or open ended cavities have been used to measure electrical properties of particular materials. However, such probes are limited in their ability to penetrate a material and generally only measure the material's outer layers. Use of data generated by these probes can lead to erroneous calculations when a structure being measured comprises multiple layers of different materials or when there are variations in material density.